Acute ischemic stroke is now a treatable condition with the thrombolytic, tissue plasminogen activator (tPA). However, tPA is far from being optimal as a therapeutic agent because it produces complete resolution of symptoms in up to 38% of patients, leaving over 60% of patients without full recovery following a stroke. Thus, even with tPA as an FDA-approved therapy, the morbidity rate following a stroke remains high. There is a need for additional treatment modalities that can be used as a monotherapy or in combination with a thrombolytic such as tPA. NMDA antagonists represent such a method to reduce the effects of ischemia-induced excitotoxicity so that the result is improved clinical scores. There are three main objectives of these proposed experiments. First, using a rabbit embolic stroke model, we will directly compare the pharmacological profiles of three novel NMDA antagonists, the uncompetitive NMDA antagonist memantine, which was recently approved for the treatment of Alzheimer's disease because of beneficial effects and a good safety profile, 3-alpha-ol-5-beta-20-one hemisuccinate, a neuroactive steroid that is a negative modulator of the NMDA receptor and (2S*,3R*)-1-(phenanthrene-2-carbonly) piperazine-2,3- dicarboxylic acid a NR2C/NR2D-preferring competitive NMDA receptor antagonist. Second, since tPA therapy is the current standard of care, it is almost certain that NMDA antagonists will be administered in combination with the thrombolytic. We will conduct combination studies to see if tPA and NMDA antagonists produce beneficial effects when administered together. In these studies, we will investigate the relationship between behavior, cell survival (TTC staining) and brain edema. Also, since the most feared complication of tPA therapy is intracerebral hemorrhage, we will investigate whether NMDA antagonists alters this relationship using a rabbit large clot embolic stroke model. As a third objective, we will test the proteomics-derived hypothesis that the AGE-RAGE pathway is involved in neurodegeneration following an embolic stroke. Preliminary evidence shows that aldolase reductase (AR) is increased in cortical tissue following embolic strokes, an increase that is attenuated by memantine administration. We will continue to use state-of-the-art proteomic techniques such as differential in-gel CyDye protein labeling technology to determine changes in protein amount in order to identify signaling pathways that mediate cell damage associated with ischemic stroke and NMDA-induced neuroprotection. These detailed pharmacological and pharmacogenomics studies should provide insight into the possible use of novel NMDA antagonists to treat acute ischemic stroke and supply valuable preclinical information necessary to initiate clinical trials. Moreover, the studies will help us identify new molecular targets for future, more specific therapies for acute ischemic stroke.